1. Field of the Invention
The present invention relates to an antenna apparatus which requires a radiation level to a direction of a low elevation angle, such as antenna apparatus employed for mobile phones utilizing satellites or the like.
2. Description of the Prior Art
FIGS. 8A-8C are schematic diagrams showing the construction of a conventional antenna apparatus disclosed in JP-A-2/219306. FIG. 8A is a sectional view of the antenna apparatus; FIG. 8B is a front view of a dielectric substrate 4 seen from side A in FIG. 8A; FIG. 8C is a front view of a dielectric substrate 3 seen from side B in FIG. 8A. In the drawings, numeral 1 designates a feed radiating element; numeral 2 designates a no-feed radiating element; numeral 3, 4 designate dielectric substrates; numeral 5 designates a ground plate; numeral 6 designates an air layer; numeral 7 designates a feeding line; numeral 8 designates a feeding connector. The air layer 6 is maintained by a structure such as spacer which keeps almost a constant interval between dielectric substrates 3, 4.
Next, the operation will be described.
The feed radiating element 1 is driven by radio waves which are fed through the feeding connector 8 and feeding line 7. The radio waves radiated from the driven feed radiating element 1 are electromagnetically coupled to the no-feed radiating element 2, thus driving the no-feed radiating element 2. The driven no-feed radiating element 2 radiates, spatially, the radio waves.
In such a conventional antenna apparatus, thickness dimensions t.sub.c1, t.sub.c2 shown in FIGS. 8A-8C are determined based on operation bands and reflection losses required for the antenna apparatus. Generally, when the upper limit of a desired reflection loss is determined, the operation band can be widened by extending the interval t.sub.c1 between the ground plate 5 and feed radiating element 1, or the interval t.sub.c1 +t.sub.c2 between the ground plate 5 and no-feed radiating element 2. For this reason, in the conventional antenna apparatus, many antennas are manufactured based on the thinnest dimension within the limits of achieving desired operation band and low reflection loss.
In addition, the smaller the dielectric constant inside the antenna, the smaller the quality factor Q of the antenna. Accordingly, a desired operation band can be achieved by a thinner thickness of the antenna, and also a larger design of the radiating element radiates intensively in a front direction of the antenna. For this reason, the following examples are frequently conducted: a dielectric formed inside the antenna such as the dielectric substrate 3 is made by a material with low dielectric constant such as foam material; constituted such that a ratio of the thickness t.sub.c1 of the dielectric substrate 3 to the thickness t.sub.c2 of the air layer 6 is enlarged.